What are the opportunities to reduce variability in apple tree productivity through targeted (sub-block) water and nutrient application?

Most of New Zealand's apple production occurs on soils which have formed from alluvial (river movement) deposits. These soils range from clays to sand, to gravels. As a result, orchard blocks can have considerable variation in soil composition and texture running through them. This project was initiated to look at variation in an orchard block with varying soil textures, correlate the variation to soil texture, and consider if variable fertiliser and irrigation applications are warranted within the block. Although there was large variation in soil texture and tree biomass between and within blocks, we could not confidently link soil texture with tree growth or productivity. However, trees on the Hau soil type were smaller, less vigorous and more productive. The inability to link soil texture with tree growth or productivity may be because orchard management tended to oversupply inputs to avoid areas of deficiency that might cause reduced productivity. Consequently, the concept of supplying variable fertiliser and irrigation applications within the block to mitigate soil texture based deficiencies is unlikely to have any positive effect on productivity under the current management practices. However, if management objectives were to shift towards minimizing inputs, a situation easily conceivable under improved ecological sustainability targets, application of nutrition or irrigation at a sub-block level, possibly based on soil texture, may become feasible and desirable.